1. Field of the Invention
This invention relates in general to earth boring bits, especially to those having improvements to exclude detritus from the seal systems that retain lubricant around the bearing shafts of drill bits with rotatable cuutters.
2. Description of the Prior Art
Earth boring bits of the type with rotatable cutters commonly have lubrications systems that include a hydrostatic pressure compensator and pressure relief means, as shown in U.S. Pat. No. 4,276,946, Biased Lubricant Compensator For An Earth Boring Drill Bit, July 7, 1981. The most successful seal system is disclosed in U.S. Pat. No. 3,397,928, Seal Means For Drill Bit Bearings, Aug. 20, 1968.
There have been suggestions for additional rings that should help protect the seal means from the detritus in the drilling fluid surrounding the bit. U.S. Pat. No. 4,168,868, Sealing System For An Earth Boring Cutter, Sept. 25, 1979 discloses a washer ring located exterior of each O-ring type seal to act as a barrier to detritus, the washer preferably being semicircular or semi-ellipitcal in cross section.
Another form of seal protector is disclosed in U.S. Pat. No. 4,194,795, Seal Protector For A Sealed Bearing Rock Bit, Mar. 25, 1980. This protector extends across the clearance between the seal and the gland, and includes among other features, an inner contoured face having a low coefficient of friction to mate with the exterior of the seal to reduce friction.
U.S. Pat. No. 4,209,890, "Method of Making A Rotary Rock Bit With Seal Recess Washer", July 1, 1980, discloses a sealing system that includes a barrier to the pulverized cuttings and other materials in the borehole, which in its preferred form is a protective washer positioned outside an O-ring seal element in the gap between the base of rolling cone cutter and the body of the bit. Protective washers are provided in numerous thicknesses, and upon determination of the size of the gap, a washer is selected that will allow the gap to be narrowed to a size that will restrict passage of most of the abrasive particles in the drilling fluid. However, the size of the gap may be expected to increase as the cone moves axially on the bearing shaft during drilling. The protective washer is pressed into a recess in the cone mouth opening of the rolling cone cutter.